When casting metals and especially when casting metals in a continuous operation, the material from which the mold or die is made is of very great importance. Because the duration of casting and thus the success and economy of the casting process are related to the mold or die life, a long lasting mold or die is a very important element in the continuous casting process.
The duration of casting relates also to the start-up problems when a new die must be substituted, the variability of the cast as a result of die performance, and the ability to cast different types of alloys. When continuously casting metals of melt temperatures, such as copper and copper alloys of various types, it has been found that graphite molds or dies are conventionally preferred as the desirable material. However, graphite molds or dies have a working life which greatly depends on the durability of their surfaces in the area directly exposed to a molten metal. Inasmuch as the molds are prepared from carbonaceous aggregates under conditions well known in the art such as shown in U.S. Pat. No. 3,794,102, these aggregates have interstitial spaces. These spaces are often the sites for mold or die failure, i.e., the mold or die surfaces start to deteriorate and the quality of the mold suffers. As a result, the premature failure of continuously cast strand is experienced. As each breakage and interruption is a time consuming operation and the start-up problems often generate additional consequences, the desideratum in the art has been to extend the die on mold life as long as possible.
Thus, in U.S. Pat. No. 3,794,102, the various prior art attempts have been disclosed, such as, lubrication of the mold and the failures associated with lubricants, for example, solids, e.g., carbon black, oils, and liquids including viscous substrates such as tallow.
With respect to the improvement in the art, the above-mentioned patent proposed the impregnation of the graphite mold material with a glass or a flux. The glass and flux operates as a lubricant and softens or melts below the solidification temperature of the metal sought to be cast.